This is what I would do,

First you need a transit to make sure that you can have at least .5 slope.

Run a 1.25 at least 1500 feet and then 1 inch the rest. no dry line necessary.

key is to not have sags. you may need to run 2 wires on the 1.25 to help with that. With the bigger pipe you can overcome the necessity for wet dry, as you are only doing one row. put in posts where necessary every 10-15-20 feet apart, enough to keep out sags..... very important no sags. You may have to put in a sap ladder somewhere in the middle to make it easier.

Hope this helps.